Metal foils have long been used for making containers and tubes for packaging and dispensing various products, including paste-type products. Such containers and tubes have frequently been made from a single foil layer. However, containers and tubes made from metal foil have had several disadvantages compared to containers made of plastic. Metal tubes tend to dent and deform more readily, crack with a moderate amount of flexure and they are more expensive.
More recently, a large share of the tube market has been taken by flexible sheet structure materials having a multiplicity of polymeric layers. Typically, such tubes have an inner heat sealable layer, an outer heat sealable layer, and a barrier layer interposed therebetween. Additional layers may be used in conventional structures to provide other properties or qualities.
Layers of a non-polymeric nature, such as paper and thin metal foils, may also be included in these sheet materials to provide specialized performance functions. It is known, for example, to provide a layer of thin aluminum foil as a high quality barrier layer. When foil is used, it is common practice to use a highly adherent polymer to adhere the foil to its adjacent layers. While such structures have had some success in the commercial market place, they have exhibited certain disadvantage which have limited their use.
Certain products are particularly hard to hold because of their chemical activity in attacking the inner tube layers and particularly the aluminum foil layer. This problem has been addressed by using chemically-resistant polymers as the tube interior layer to protect the foil. In order to alleviate this problem, commonly assigned, copending application Ser. No. 306,675 discloses the use of linear low density polyethylene as the innner sealant layer of the tube.
It is also known to provide a layer of paper for imparting dimensional stability, which is particularly important for printing, and which also provides an aesthetically pleasing and aseptically clean appearing white background. The inclusion of a paper layer also improves the deadfold retention properties of the tube.
Tube failure is generally attributed to their rough handling during shipment, as a result of which the tube sidewall splits, allowing the contents to ooze out. It has been observed that the paper layer in the laminate is the weakest part of the structure, and once it begins to fail, the entire tube is weakened and breaks.
The ability of a tube to withstand rough handling is related to its ability to withstand "drop test", hereinafter also described as "tube drop test", in which a tube filled with product is repeatedly dropped until it fails. All tubes shipped in commerce may be expected to be subjected to rough handling, essentially independent of the product contained therein, and are thus subject to handling stresses as encountered in the tube drop test. Economical construction of tubes which are consistently capable of passing the tube drop test has remained a problem. This problem has been addressed by using a reinforcing layer of a biaxially oriented polypropylene in the interior of the sheet structure, as described in said commonly assigned copending application Ser. No. 306,675. The structure disclosed in said copending application, however, contains paper, and while certain improvements in strength are realized in such structures, it is desirable to provide other structures which afford the dimensional stability and economy of such paper-containing structures, and which also have increased strength and other improved attributes.
Improvement in preventing chemical attack by the product in the container is described in another commonly assigned copending application Ser. No. 340,468, in which a polyacrylic acid chrome complex primer is used between the foil and the ethylene acrylic acid copolymer on the sealant side of the foil.
It is therefore an obJect of the present invention to provide a dimensionally stable multi-layer structure without a paper layer.
It is further object of this invention to provide such paper-free, multi-layer laminates for making tubes which are resistant to chemical attack by products of the type packaged in dispensing containers.
It is also an object of this invention to provide containers and tubes having acceptable deadfold and crease retention properties.
The foregoing and other advantages and features of the invention will be more fully appreciated from the ensuing detailed description and the accompanying drawings.